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03-01-2015, 06:35 PM
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Join Date: Nov 2008
Location: Shreveport, LA
Posts: 1,002
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Is this switch sufficient to be an Avionics Master Switch
I have decided I want an avionics master switch. Foregoing the debate as to whether this is a good idea or not, my question is about the switch I have selected. Specifically, do you think this switch is appropriate for an avionics master switch. My avionic breakers add up to 26 amps. If not, do you have a recommendation for an avionics switch?
http://www.alliedelec.com/nkk-switch...259/#tab=specs
Here are the specs on it:
Body Style : Rectangular
Contact Form : DPST
Current, Rating : 30 Amps
Mounting Hole Size : 23 x 37 mm
Mounting Type : Panel
Number of Poles : 2
Number of Positions : 2
Operation : On-None-Off
Standards : UL CSA
Termination : Screws
Type : Rocker
Voltage, Rating : 250 VAC
Last edited by blueflyer : 03-01-2015 at 07:02 PM.
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03-01-2015, 07:01 PM
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Join Date: Jan 2005
Location: Victoria, Canada
Posts: 2,247
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According to Mouser, this switch has been discontinued by the mfr.
Your call.
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RV-9A complete
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03-01-2015, 07:03 PM
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Join Date: Jan 2005
Location: NC25
Posts: 3,503
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All I can say is that the SPEC you list is for AC voltage. You have DC voltage in your aircraft. ANY switch that has a larger DC amperage than the sum of all the DC current will work.
The PDF link to the DATASHEET has a DC rating at 30 Volts that equals the 125 VAC current resistive rating so it appears that it will be ok.
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Gary A. Sobek
NC25 RV-6 Flying
3,400+ hours
Where is N157GS
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To most people, the sky is the limit.
To those who love aviation, the sky is home.
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03-01-2015, 10:10 PM
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Join Date: Apr 2008
Location: Riley TWP MI
Posts: 3,068
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A general rule of thumb is that any SNAP action AC switch can handle the same current at 12 VDC that it can handle at 120 VAC. The actual loads should be added up, not the breaker sizes.
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Joe Gores
RV-12 Flying
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03-01-2015, 11:43 PM
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Senior Curmudgeon
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Join Date: Sep 2005
Location: Dayton Airpark, NV A34
Posts: 15,408
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I have used switches similar to this, I used a jumper between the two sides to turn it into what is effectively a SPST switch---------the two sides share the load.
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Mike Starkey
VAF 909
Rv-10, N210LM.
Flying as of 12/4/2010 
Phase 1 done, 2/4/2011
Sold after 240+ wonderful hours of flight.
"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
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03-02-2015, 12:00 AM
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Join Date: Jan 2005
Location: 57AZ - NW Tucson area
Posts: 10,011
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Quote:
Originally Posted by vlittle
According to Mouser, this switch has been discontinued by the mfr.
Your call.
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The manufacturer still has it as a valid switch on their web site.
https://www.nkkswitches.com/partsear...?search=SW3821
Mouser only seems to order 9 at a time, other distributers have much more stock on hand.
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Gil Alexander
EAA Technical Counselor, Airframe Mechanic
Half completed RV-10 QB purchased
RV-6A N61GX - finally flying
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La Cholla Airpark (57AZ) Tucson AZ
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03-02-2015, 12:41 AM
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Join Date: Dec 2011
Location: Livermore, CA
Posts: 6,767
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Quote:
Originally Posted by Mike S
I have used switches similar to this, I used a jumper between the two sides to turn it into what is effectively a SPST switch---------the two sides share the load.
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Mike, this doesn't always work. One, the current will only split 50-50 if the two switches have exactly the same resistance. Two, the critical part for a dc switch is opening (disconnect) when there's a tendency to draw an arc. One switch will nearly always open first, putting the entire opening load on the other. |
03-02-2015, 06:19 AM
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Join Date: Nov 2008
Location: Shreveport, LA
Posts: 1,002
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a few people have brought up things I hadn't considered, so maybe I should sit down and read a little more before I decide on an appropriate avionics master switch.
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03-02-2015, 07:24 AM
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Join Date: Mar 2008
Location: Dublin, CA
Posts: 1,259
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Or you could just use the switch to enable a continuous duty contactor. Then the switch current isn't important. The 30A is switched by the contactor not the switch. Then you can pick a switch that matches your panel.
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Ray Tonks
2020 Donation Paid
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03-02-2015, 08:31 AM
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Join Date: Apr 2008
Location: Riley TWP MI
Posts: 3,068
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Read these articles by Bob Nuckolls. Avionics Master Switches: Really Necessary? If you really have to have an avionics switch, Bob Nuckolls offers a safe way to wire it without a single point of failure.
How the avionics switch was born
Bob Nuckolls is an engineer who has worked for major aircraft companies. He wrote the book on how to wire airplanes. The majority of E-AB airplanes are wired according to his book. Bob Nuckolls has served as an expert witness in aviation accident lawsuits. I admire his electrical and electronic knowledge.
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Joe Gores
RV-12 Flying
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